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Argument 30
The article entitled 'Eating Iron' in last month's issue of Eating for Health reported that a recent
study found a correlation between high levels of iron in the diet and an increased risk of heart
disease. Further, it is well established that there is a link between large amounts of red meat in
the diet and heart disease, and red meat is high in iron. On the basis of the study and the
well-established link between red meat and heart disease, we can conclude that the
correlation between high iron levels and heart disease, then, is most probably a function of the
correlation between red meat and heart disease. The following appeared as a letter to the
editor of a national newspaper.
In this argument the author dtes a study correlating the amount of iron in a person's diet with
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the person's risk of heart disease. The author also cites a well-established correlation between
diets that indude large amounts of red meat, which is high in iron, and the incidence of heart
disease. The author concludes that the correlation observed in the study is a function of the
correlation between read meat and heart disease. This argument suffers from a series of poor
assumptions, which render it wholly unpersuasive as it stands.
To begin with, the author provides no evidence that the study's results are statistically
reliable. In order to establish a strong correlation between dietary iron and heart disease, the
study's sample must be suffident in size and representative of the overall population of
heart-disease victims. Lacking evidence of a suffidenfly representative sample, the author
cannot justifiably rely on the study to draw any conclusion whatsoever.
Even assuming that the study is statistically reliable, a direct correlation between a high-iron
diet and heart disease does not necessarily prove that the former causes the latter. While a
high correlation is strong evidence of a causal relationship, in itself it is not suffident. The
author must also account for all other possible factors leading to heart disease, such as
genetic propensity, amount of exercise, and so forth. Lacking evidence that the heart-disease
sufferers whom the study observed were similar in all such respects, the author cannot
justifiably conclude that a high-iron diet is the primary cause, or even a contributing cause, of
heart disease.
Similarly, a correlation between a diet, which includes large amounts of red meat and heart
disease, does not necessarily infer a causal relationship. Lacking evidence to the contrary, it is
possible that red-meat eaters are comparatively likely to incur heart disease due to factors that
have nothing to do with the amount of red meat in their diet. Perhaps red-meat eaters are the
same people who generally overeat, and it is obesity rather the consumption of red meat
specifically that causes heart attacks. The author must consider and eliminate this and other
possible reasons why red-meat eaters are more likely than other people to suffer from heart
disease. Otherwise, I cannot accept the author's implidt daim that eating red meat is any more
likely to cause heart disease than eating other foods.
Even assuming that a high-iron diet, including a diet high in red meat, promotes heart
disease, the author cannot reasonably conclude that this causal relationship fully explains the
study's results. The author overlooks the possibility that other foods are also high in iron, and
that the study's participants ate these other foods as well as, or instead of, red meat. Without
accounting for this possibility the author cannot convincingly conclude from the study that red
meat is the chief cause of heart disease.
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